Researchers have observed anorexia and weight loss or reduction in weight gain in humans and animals that have been exposed to immune stimulants, such as endotoxin (LPS). The intraperitoneal injection of lipopolysaccharide (i.e. endotoxin) into chickens decreases food intake and growth rate for 24 hours, alters nutrient metabolism, and induces fever.
Recent studies (Klasing et al., 1987, J Nutr. 117:1629) have confirmed that the vaccination of domestic fowl with several immune stimulants also can result in a substantial reduction in feed intake and induce weight loss or decrease in weight gain. In a study recently conducted with white Pekin ducks, two vaccinations reduced final carcass weight by as much as 0.4 lbs./bird and breast meat by 0.075 lbs./bird. Broilers and Single Comb White Leghorns (egg laying chickens) also have been observed to have reduced weight gains following immune stimulation. The potential losses due to immune stimulation costs the poultry industry millions of dollars per year. At the present time, antibiotics are used to prevent such weight loss, but the use of antibiotics for this purpose is expensive and not without disadvantages.
In a similar manner anorexia, weight loss, and reduced growth of humans that are subjected to chronic immune stimulation because of infections, surgery, or exposure to immune stimulants is devastating to health and well being.
The mechanism by which immune stimulation causes anorexia, weight loss and reduced growth is known to be mediated by products, such as catabolic hormones, released following immune stimulation (e.g., the macrophage cytokine known as interleukin-1 or IL-1). The production of IL-1 from macrophages simultaneously stimulates T-cells to release IL-2, an anticarcinogenic compound which is desirable, but the release of IL-1 and other catabolic hormones from stimulated macrophages and possibly other immune-regulated cells induces an undesirable systemic reduction in skeletal muscle synthesis and increased muscle degradation resulting in weight loss or a decline in weight gain. Thus, while IL-1 and related immune hormones are essential cytokines for immune function, their systemic hormonal effects are devastating and have prevented its acceptance for immune therapy.
It is known that other biological products produced by immune cells, such as tumor necrosis factor (TNF) also can cause adverse physiological changes in animals, including anorexia and cachexia, and it has been observed that viral infections of animals can have similar adverse effects on the animals. It also has been observed that viral infections, especially HIV infections, can undesirably deplete the CD-4 (helper T cells) and CD-8 (cytotoxic T cells) cell populations in infected animals, including humans.
It would be advantageous to have methods of maintaining or elevating CD-4 and CD-8 cell populations in animals to bolster or benefit their immune systems and methods for preventing or alleviating the adverse effects of the production or exogenous administration of TNF and viral infections in animals.